One piece watertight concrete structure

ABSTRACT

A manufacturing process for a one piece tank that involves three steps results in a consistently watertight and structurally stronger unit than previous tanks. The three steps comprise a process for producing the body of the tank, a process for producing a preliminary lid, and a process for producing the final tank. An important step in the process for producing the body of the tank is extending reinforcing steel (rebar) a distance above the concrete walls of the tank. After the preliminary lid is placed into a groove of the tank, the rebar is bent over the lid and a water stop is applied between the walls of the tank and the preliminary lid. The water stop can be any of several forms. In one form, the water stop is in the form of butyl or rubber strip which projects from the walls of the tank above the walls with the rebar. In an alternate form, the water stop is in the form of a gasket of plastic or other suitable material inserted in a groove at the top of the tank. Once the preliminary lid is in place and the rebar bent over the preliminary lid, reinforcing steel (rebar) is bent over the preliminary lid and secured to proper locations. Then concrete is poured to the top and above the sidewalls of the tank until completely full. The resulting cured structure is a one piece water tight tank with an integral water stop.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/223,600 filed Jul. 29, 2016, now U.S. Pat. No. 10,501,349, whichclaimed priority to U.S. Provisional Patent Application Ser. No.62/318,887 filed May 31, 2016, by Thomas Henry Jarrett for “One PieceWatertight Concrete Structure.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention generally relates to concrete structures used inonsite sewage facilities (OSSFs) and, more particularly, to a one piecewatertight concrete structure having specific application as a septictank in an OSSF and to a method of manufacture of a one piece watertightconcrete structure.

Background Description

A septic tank is a key component of a small-scale sewage treatmentsystem common in areas that lack connection to main sewage pipesprovided by local government or private corporations. The term “septic”refers to the anaerobic bacterial environment that develops in the tankwhich decomposes the waste discharged into the tank.

Precast concrete tanks have been manufactured for over 50 years for usein wastewater and related industries. Initially, these tanks weremanufactured in several pieces with the pieces sealed at the job site.As watertight regulations increased, tank production evolved to topseamed tanks that are sealed at the manufacturer. While this is animprovement, it is still not a guarantee that the tanks would not leak.Leaks might be caused by shifting soil, high water tables, and internalwater testing pressure.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodof producing precast concrete tanks that results in a one piecewatertight tank with no joints to seal.

According to the invention, there is provided a manufacturing processthat involves three steps and results in a consistently watertight andstructurally stronger unit than previous tanks. The three steps comprisea process for producing the body of the tank, a process for producing apreliminary lid, and a process for producing the final tank. Animportant step in the process for producing the body of the tank isextending reinforcing steel (rebar) a distance, on the order of 18″,above the concrete walls of the tank. When the preliminary lid is placedinto a groove of the tank, the rebar is bent over the preliminary lidand a water stop is applied between the walls of the tank and thepreliminary lid. The water stop can have any of several forms. In oneform, the water stop is in the form of butyl or rubber strip whichprojects from the walls of the tank above the walls with the rebar. Inan alternate form, the water stop is in the form of a gasket of plasticor other suitable material inserted in the groove of the tank. Once thepreliminary lid is in place and the rebar bent over the preliminary lid,reinforcing steel (rebar) is placed on the preliminary lid and securedto proper locations. Then concrete is poured to the top and above thesidewalls and endwalls of the tank until completely full. The resultingcured structure is a one piece water tight tank with an integral waterstop.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects and advantages will be betterunderstood from the following detailed description of preferredembodiments of the invention with reference to the drawings, in which:

FIG. 1 is a cross-sectional view of a typical septic tank known in theprior art;

FIG. 2 is a cross-sectional view of the precast concrete septic tankmanufactured according to the present invention;

FIG. 3 is a plan view of the precast concrete septic tank manufacturedaccording to the present invention;

FIG. 4 is a simplified plan view of the tank body as manufacturedaccording to the first step in the process according to the invention;

FIG. 5A is an enlarged partial cross-sectional view showing the waterstop according to one embodiment of the invention; and

FIG. 5B is an enlarged partial cross-sectional view showing the waterstop according to an alternate embodiment of the invention.

DETAILED DESCRIPTION THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, there isshown in cross-section a conventional septic tank 10. One end of thetank 10 is connected to an inlet waste water pipe 11 and the other endto an outlet pipe 12 that is connected to a septic drain field.Generally, these pipe connections are made with a “T” pipe allowingliquid to enter and exit without disturbing any crust on the surface.The tank usually incorporates two chambers 13 and 14, each equippedwith, e.g., a manhole cover 15 and 16 and separated by a dividing wall17 with openings 18 located about midway between the floor and roof ofthe tank.

Wastewater enters the first chamber 13 of the tank, allowing solids tosettle and scum to float. The settled solids are anaerobically digested,reducing the volume of the solids. The liquid component flows throughthe dividing wall 17 into the second chamber 14 where further settlementtakes place. The excess liquid, now in a relatively clear condition,then drains from the outlet 12 into the septic drain field.

The problem solved by the present invention relates to the manner inwhich the lid 19 is attached to the bottom of the tank. On the one hand,the lid and tank have been sealed at the job site, but the quality andintegrity of the seal varied greatly. An improvement resulted in theseal being made by the manufacturer, assuring a more uniform quality ofthe seal. Even so, the resulting structure is inherently a two-piecestructure having a seal that can, under certain conditions, leak. Forexample, the seals might leak due to shifting soil as a result of aload, such as a truck or other heavy equipment passing over the sitewhere the tank is buried, high water tables, and internal water testingpressure.

The solution to this problem according to the present invention is amethod of manufacturing a one piece precast concrete tank which is watertight and structurally stronger than conventional tanks and thereforeresistant to shifting soil, high water table of internal water testingpressure. A tank manufactured according to the present invention isillustrated in FIGS. 2 and 3, to which reference is now made. As shownin these figures, the completed one piece tank 20 comprises a tank body21 integral with a tank lid 22. The method of making this one piece tankbegins with the process of producing the body of the tank. This processincludes preparing the tank form, which involves cleaning and oiling theform to facilitate release of the tank body after the concrete hascured. Reinforcing steel (rebar) is placed into the outside jacket form.At least some of the rebar extends on the order of 18″ above thefinished edge of the tank body. Hole formers, for inlet and outletholes, and adapters are placed in proper locations. Then the core formis placed inside the outer jacket form. Once the core form is in placeand all latches and fasteners are checked for security, concrete ispoured into the form to the proper level. Concrete is preferably of noless than 4500 psi is used in forming the body of the tank andpreferably the body of the tank is formed to be at least four inchesthick. FIG. 4 is a simplified plan view of the top of the body of thetank 21 showing a groove 23 formed in the upper edges of the side wallsof the tank body.

The second step of the method of manufacturing the tank according to theinvention is the process of preparing the preliminary lid. The lid formis prepared by cleaning and oil to facilitate the release of the curedpreliminary lid. Hole formers, for the manholes and other holes, areplaced in the lid form along with risers and/or adapters in properlocations for access. Rebar is placed in th preliminary lid form.Concrete of no less than 4500 psi is then poured to a level of abouthalf that of the finished lid and allowed to cure.

The final step in the method according to the invention is theprocessing of the final tank. After the tank body has cured, the core ofthe form is removed. The preliminary lid is removed from the lid formand placed into the groove 23 of the tank body. After setting thepreliminary lid in the groove, the rebar is bent over the lid.

An important feature of the invention is the formation of the water stopwhere the lid joins the body of the tank. In one embodiment shown inFIG. 5A, the water stop is in the form of a butyl or rubber strip 51.This strip is placed in the tank body form about the top edge andextends above the top edge of the poured concrete. As shown in FIG. 5A,the strip 51 extends above the edge of the tank 21 adjacent to the rebar52 which is bent over the preliminary lid. Alternatively, a plastic bandor gasket can be inserted into the top of the concrete. At this point,reinforcing steel (rebar) is bent over the preliminary lid and securedto proper locations. Then, concrete is poured on the top and above thesidewalls and end walls of the tank body, so that the water stop isfully incorporated into the resulting one piece unit with no joints toseal.

In an alternate embodiment, as shown in FIG. 5B, a gasket 53 of plasticor suitable material is first formed in the groove 23 of the tank bodybefore the preliminary lid is set into the groove. Once the preliminarylid is placed in the groove, the rebar 52 is bent over the preliminarylid and reinforcing steel (rebar) is placed onto the preliminary lid andsecured to proper locations. Then, concrete is poured to the top andabove the sidewalls and end walls of the tank body, so that the waterstop is fully incorporated into the resulting one piece unit with nojoints to seal.

While the invention has been described in terms of preferredembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theappended claims.

The invention claimed is:
 1. A manufacturing process producing a onepiece watertight precast concrete tank comprising the steps of:producing a body of the tank having side walls and end walls by pouringconcrete into a space between a tank form and a core into whichreinforcing steel has been placed, the reinforcing steel extending apredetermined distance above a finished level of the side walls and endwalls of the body of the tank, the body of the tank being formed with agroove about an upper edge of the side walls and end walls of the bodyof the tank; producing a preliminary lid by pouring concrete into a formto a first level which is less than a finished thickness of a lid; andproducing a final tank by placing the preliminary lid in the grooveformed about top edges of the side walls and end walls of the body ofthe tank and bending the reinforcing steel over the preliminary lid andadding additional reinforcing steel to the preliminary lid beforepouring concrete on top of the preliminary lid and above the side wallsand end walls of the body of the tank until the form is completely full.2. The manufacturing process according to claim 1, wherein a water stopis formed by incorporating a strip of water impervious material into thetop edges of the side walls and end walls of the body of the tank andprojecting above the top edges of the side walls and end walls, theprojection of the strip of water impervious material being incorporatedinto a finished top when the concrete is poured over the preliminarylid.
 3. The manufacturing process according to claim 2, wherein thewater impervious material is butyl or rubber.
 4. The manufacturingprocess according to claim 1, wherein a water stop is formed by applyinga gasket of water impervious material to the groove of the body of thetank before placing the preliminary lid in the groove of the body of thetank.
 5. The manufacturing process according to claim 1 wherein theproducing the body of the tank step is performed by using concrete of atleast 4500 psi when pouring the concrete.
 6. The manufacturing processaccording to claim 1 wherein the space in the first producing step is atleast four inches wide so as to produce the tank body having the sidewalls and end walls at least four inches thick.
 7. The manufacturingprocess according to claim 1 further comprising a step of incorporatinga water stop in the body of the tank and the lid outside of thereinforcing steel which extends from the body of the tank and is bentinward in the lid.